JP2014170148A - Optical module and scanning type image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical module that reduces a deviation generated at a relative position of a three-color beam spot because a position of an emission point of light displaces respectively when a plurality of lasers are driven in an optical module.SOLUTION: An optical module has a plurality of lasers loaded, and radiates beam light from the plurality of lasers. The optical module includes a mirror 2b through which a red laser 1a passes, and upon which a green laser 1b and a blue laser 1c reflect. The mirror 2b is attached at two attachment section portions 31a and 31b different in a material.

Description

  The present invention relates to an optical module and a scanning-type image display device, for example, an optical module that emits light beams from a plurality of lasers aligned on one optical axis, and an image display of the light beams from the optical module. The present invention relates to a scanning image display apparatus.

  In recent years, development of small projectors that can be easily carried around and that can be displayed on a large screen has been active. Small projectors that can be connected to notebook PCs and video cameras with built-in projectors that can project recorded images are already on the market, and those built into mobile phones and smartphones are expected to appear in the future.

  As a projector method, a type in which a lamp or LED is used as a light source and an image displayed on a liquid crystal panel or a digital micromirror device (DMD) is projected has preceded, but a laser is used as a light source. Development of laser projectors (scanning image display devices) that scan and display beam light with a movable mirror is also underway. Since laser light is used as the light source, focusing is not necessary, and it is easy to increase the brightness of the image, and it is considered suitable for use in projecting onto a handy wall on the go.

  In addition, it is also considered to develop a head-up display such as a display on a windshield, navigation display, etc., which is mounted on an automobile using the high brightness of the image.

  Uses red, green, and blue lasers, and has a beam combiner that combines the laser beams of three colors into a combined beam that travels along one axis, and a beam scanner that scans the deflection direction of the combined beam A configuration of a scanning image display apparatus that can display a color image is described in, for example, Japanese Patent Application Laid-Open No. 2011-64926 (Patent Document 1). Patent Document 1 describes that the position of the dichroic mirror does not change by reducing the thickness of the housing to which the dichroic mirror is attached as the distance from the laser decreases.

JP 2011-64926 A

  In the scanning image display apparatus as described above, it is important to match the optical axes of the three color light beams with high accuracy and to keep the optical axes against disturbance due to changes in operation and environmental temperature. If the optical axis is deviated, there is a problem that the relative position deviation occurs in each color spot on a display area such as a screen, and the image is blurred.

  Therefore, when assembling the optical module, it is necessary to adjust and assemble so that the optical axes of the three colors are matched. Further, when the scanning image display device is used, the temperature rises due to the heat generated by the laser and thermal deformation occurs, so that it is necessary to consider the deviation of the optical axis due to the positional deviation of the optical components during the thermal deformation.

  As a laser used for the light source, a cylindrical metal package product called a CAN package is mainly used. A semi-cylindrical heat sink is connected to the tip of a cylindrical base, and a laser chip is joined to a flat surface of the heat sink via a submount and covered with a cap.

  In such a laser, there is a problem that the position of the light emitting point is displaced due to deformation due to temperature rise. This is because uniform thermal deformation does not occur due to the difference in thermal expansion coefficient between the base and the heat sink or the difference in thermal expansion coefficient between the laser chip and the submount and the heat sink. The optical axis direction of the beam light from the laser is a direction connecting the light emitting point of the laser and the lens. Therefore, if the position of the light emitting point is displaced, the optical axis of the beam light is shifted. Since the lasers of the three colors red, green, and blue have different laser structures, the displacement of the position of the light emitting point is different for each laser. In particular, at the time of the present invention, the structure of the red laser is greatly different from that of the other two colors of green and blue compared to the laser. Specifically, the length of the laser chip of the red laser is about twice as long, and accordingly, the length of the semi-cylindrical heat sink or submount is about twice as long. For this reason, the displacement of the light emitting point is about twice as large as that of the other blue and green lasers. The configuration considering the displacement deviation of the emission point of the red laser is not taken, and there is a problem of deviation of the emission point position.

  An object of the present invention is to provide a small-sized optical module and a scanning image display device having an optical component mounting structure that can reduce a spot relative position shift on a display area such as a screen.

  In order to solve the above problems, for example, the configuration described in the claims is adopted.

  The present application includes a plurality of means for solving the above-described problem. For example, in an optical module that includes a plurality of lasers and that emits light beams from the plurality of lasers, the first laser includes: It has a mirror that transmits and reflects the second laser and the third laser, and the mirror is mounted with a plurality of mounting portions that are different in at least one of material and thickness.

  An optical module that mounts a plurality of lasers and irradiates light beams from the plurality of lasers includes a mirror that reflects the first laser and transmits the second laser and the second laser. The mirror is mounted with a plurality of mounting portions that differ in at least one of material and thickness.

  The first laser is a red laser, the second laser is a green laser, and the third laser is a blue laser.

  According to the present invention, when the temperature rises or falls due to heat generated during laser driving, the direction of deviation of the laser optical axis caused by the thermal deformation of the laser is changed with respect to the plurality of laser light sources. Since they can be matched on the axis, it is possible to provide a scanning image display device including a laser light source module in which the relative positional deviation of the laser spot on the screen is reduced.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a first overall configuration diagram of a scanning image display apparatus according to an embodiment of the present invention. It is a perspective view which shows the general view of the laser used for the Example of this invention. The principle explanatory drawing of the light-emitting point displacement by the temperature rise of the laser used for the Example of this invention. Explanatory drawing of the optical axis offset by the temperature rise of the laser used for the Example of this invention. 1 is a plan view of a scanning image display apparatus according to a first embodiment of the present invention. It is a perspective view which shows 1st Embodiment of the attachment structure of the mirror of this invention. It is a perspective view which shows 2nd Embodiment of the attachment structure of the mirror of this invention. It is a perspective view which shows 3rd Embodiment of the attachment structure of the mirror of this invention. It is a perspective view which shows 4th Embodiment of the attachment structure of the mirror of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, since the structure which attached | subjected the same code | symbol has the same function, those description may be abbreviate | omitted when already demonstrated. Further, in the necessary drawings, orthogonal coordinate axes including an x axis, a y axis, and a z axis are described in order to clarify the description of the position of each part.

  FIG. 1 is a block diagram of a scanning image display apparatus according to a first embodiment of the present invention. In FIG. 1, an optical module 101 includes a case 9 with a red (R) laser 1 a and a green (G) laser serving as laser light sources corresponding to three colors of red (R) / green (G) / blue (B). 1b, a blue (B) laser 1c, and a laser light source module 100 having a beam coupling portion composed of a first mirror 2a and a second mirror 2b for coupling light beams emitted from the respective laser light sources are attached. The first mirror 2a reflects the blue wavelength beam and transmits the green wavelength beam, and the second mirror 2b transmits the red wavelength beam and reflects the blue and green wavelength beams. It is a dichroic mirror designed as follows. Further, a projection unit that projects the combined beam light onto the screen 109 and a scanning unit that two-dimensionally scans the projected beam light on the screen 109 are provided. The projection unit includes a quarter wavelength plate 111, an angle of view expansion element 112, and the like.

  An image input signal 116 to be displayed is input to the video signal processing circuit 103 via the control circuit 102 including a power source and the like. The video signal processing circuit 103 performs various processes on the input image signal, and then separates it into R / G / B three-color signals and sends them to the laser light source driving circuit 104. The laser light source driving circuit 104 supplies a driving current for light emission to the corresponding laser in the laser light source module 100 according to the luminance value of each signal of R / G / B. As a result, the laser emits a light beam having an intensity corresponding to the luminance value of the R / G / B signal in accordance with the display timing.

  The video signal processing circuit 103 extracts a synchronization signal from the image signal and sends it to the scanning mirror drive circuit 105. The scanning mirror drive circuit 105 supplies a drive signal for two-dimensionally rotating the mirror surface to the scanning mirror 113 in the optical module 101 in accordance with the horizontal / vertical synchronization signal. Accordingly, the scanning mirror 113 periodically rotates the mirror surface by a predetermined angle to reflect the beam light, and scans the light beam on the screen 109 in the horizontal direction and the vertical direction to display an image.

  The front monitor signal detection circuit 106 receives a signal from the front monitor 114 and detects each output level of R / G / B emitted from the laser. The detected output level is input to the video signal processing circuit 103, and the output of the laser is controlled to be a predetermined output.

  As the scanning mirror 113, for example, a biaxial drive mirror created using MEMS (Micro Electro Mechanical Systems) technology can be used. Examples of the driving method include piezoelectric, electrostatic, and electromagnetic driving methods. Alternatively, two uniaxial drive mirrors may be prepared and arranged so that the beam light can be scanned in directions orthogonal to each other. In FIG. 1, the combined beam light is sent to the scanning mirror 113 via the reflection mirror 115.

  Next, with reference to FIGS. 2 and 3, the principle of the emission point displacement due to the laser temperature rise will be described.

  FIGS. 2A and 2B are perspective views showing examples of laser structures that can be used for the red (R) laser 1a, the green (G) laser 1b, and the blue (B) laser 1c.

  In FIG. 2A, the laser is protected by a stem base 10, a stem cover 11, and a transparent window portion 12 installed at the tip of the stem cover 11. A lead 13 for feeding power to the laser is drawn behind the stem base 10.

  FIG. 2B shows a state in which the stem cover 11 and the window portion 12 are removed in order to explain the internal structure of the laser. In FIG. 2B, a heat sink 14 having a shape obtained by cutting a cylinder is joined to a columnar stem base 10, and a laser chip 16 is joined to the flat surface via a submount 15. The light emitting point at the tip of the laser chip 16 is configured to be positioned substantially on the center line of the laser. The lead 13 penetrates the stem base 10 and protrudes into the stem cover 11. The lead 13 and the laser chip 16 are connected via a wire 17. The lead 13 and the stem base 10 are sealed with an insulating sealing material 18.

As these materials, for example, the laser chip 16 is gallium arsenide, the submount 15 is aluminum nitride, the heat sink 14 is copper, the stem base 10 and the stem cover 11 are iron, the window 12 is glass, and the sealing material 18 is low melting glass. Etc. are used.

  In FIG. 2, the direction in which the laser beam is emitted is referred to as the y direction, and the direction in which the laser chip 16 is mounted on the heat sink 14 is referred to as the z direction.

  FIG. 3 is a yz plan view of a laser structure that can be used for the red (R) laser 1a, the green (G) laser 1b, and the blue (B) laser 1c.

  The broken line in FIG. 3 is the position of the laser chip 16, the submount 15 and the heat sink 14 before the laser temperature rises, and the laser emission point at that time is at the position 19. On the other hand, when the temperature rises when the laser is driven or depending on the environmental temperature, the materials of the laser chip 16, the submount 15 and the heat sink 14 are different, so that they are thermally deformed to the position indicated by the solid line in FIG. Move to position. The displacement of the light emitting point when the temperature of the laser rises indicates 21 in the figure. The light-emitting point displacement 21 is the length of the laser chip 16, the submount 15 and the heat sink 14, typically the length 22 of the heat sink 14. Here, the light-emitting point displacement 21 increases as the length 22 increases. .

  FIG. 4 is an explanatory diagram of the optical axis deviation due to the temperature rise and environmental temperature of the red (R) laser 1a, the green (G) laser 1b, and the blue (B) laser 1c.

  An optical axis 23 indicated by a solid line in FIG. 4 is an optical axis in a reference state, and is in a state during adjustment where there is almost no increase in the temperature of the laser. Therefore, the spots of the respective colors match on the screen 109.

  In contrast, when the temperatures of the red (R) laser 1a, the green (G) laser 1b, and the blue (B) laser 1c rise, the green (G) laser 1b that is a green laser and the blue (B) laser that is a blue laser. Since 1c has substantially the same laser structure, there is no difference between the emission point displacement 21b of the green (G) laser 1b and the emission point displacement 21c of the blue (B) laser 1c. Accordingly, the optical axis is not shifted, and the optical axis 24 shown by the broken line in FIG. 4 is transmitted through the first mirror 2a while the green beam is transmitted and the blue beam is reflected. On the other hand, the red (R) laser 1a, which is a red laser, has a heat sink length 22a that is approximately twice as long as the other green (G) laser 1b and blue (B) laser 1c due to the laser structure. Therefore, the emission point displacement 21a of the red (R) laser is about twice as large as the emission point displacements 21b and 21c of the green (G) laser 1b and the blue (B) laser 1c. Accordingly, the optical axis 25 of the first laser becomes as shown by the one-dot chain line in FIG. 4, and a difference between the optical axis 24 of the green (G) laser 1b and the blue (B) laser 1c, and an optical axis shift 26 occur. Due to this optical axis deviation 26, there is a problem that a relative position deviation occurs in the spot on the screen 109 and the image is blurred.

  The laser light source module 100 according to the embodiment of the present invention will be described below.

  FIG. 5 is a plan view for explaining the optical module according to the first embodiment. The second mirror 2b is attached at two attachment portions 31a and 31b. Among these, the material of one attachment part 31b differs in the material of the other attachment part 31a in a linear expansion coefficient. Due to the difference in the coefficient of linear expansion of the materials of the mounting portions 31a and 31b, the second mirror 2b has an inclination 32 (an inclination that inclines clockwise in the plane of FIG. 5) according to the temperature when the temperature rises. Since the green (G) laser 1b, which is a green laser, and the blue (B) laser 1c, which is a blue laser, have substantially the same laser structure, the emission point displacement 21b of the green (G) laser 1b and the emission point of the blue (B) laser 1c. There is no difference in displacement 21c. Accordingly, the optical axis is not shifted, and the optical axis 24 shown by the broken line in FIG. 5 is transmitted through the first mirror 2a while the green beam is transmitted and the blue beam is reflected. At this time, since the second mirror 2b has an inclination 32, the reflected light approaches the optical axis 25 of the red (R) laser 1a, which is a red laser, and there is no spot deviation on the screen 109. That is, when the tilt 32 of the second mirror 2b is generated in accordance with the temperature rise of the red (R) laser 1a, the green (G) laser 1b, and the blue (B) laser 1c and the optical axis shift 26 due to the environmental temperature. The optical axis deviation 26 can be almost eliminated with respect to the optical axis 23 which is the optical axis in the reference state.

  As a method of changing the inclination 32 of the second mirror 2b in response to the temperature rise, for example, as shown in FIG. 5, the thickness of the member of the mounting portion 31b is made larger than the thickness of the member of the mounting portion 31a. The thickness of the member 31b may be controlled, or the material of the member of the mounting portion 31b may be changed to the material of the member of the mounting portion 31a (for example, a material that is more easily expanded due to a temperature rise) as will be described later. Alternatively, both the thickness and material may be adjusted.

  With the mounting structure of the second mirror 2b, it is possible to provide a scanning image display apparatus including the laser light source module 100 in which the relative displacement of the laser spot on the screen 109 is reduced without the optical axis deviation 26.

  Here, if the guaranteed operation temperature of the laser is deviated, there is a difference in the visibility of each color due to temperature-dependent laser wavelength fluctuations, resulting in image color misregistration such as the entire screen becoming reddish. Moreover, since it becomes a factor of the fall of a laser output and life shortening, ensuring of the heat dissipation of a laser is an important subject.

  Therefore, in order to keep the laser driving within the guaranteed temperature of the red (R) laser 1a, the green (G) laser 1b, and the blue (B) laser 1c, the red (R) laser 1a, the green (G) laser 1b, and the blue ( B) The thermal resistance from the laser 1c to the case 9 may be reduced so that the case 9 serves as a heat radiating portion. In the structure, there is almost no temperature difference between the attachment portions 31a and 31b of the second mirror 2b.

  FIG. 6 shows the mounting structure of the second mirror 2b according to the first embodiment. One part of the second mirror 2b is a part of the case 9 and the other part is attached to an attachment part 31b which is a plate-like member made of a material different from that of the case 9. Here, magnesium die casting is used as the material of the mounting portion 31a, and resin is used as the material of the one mounting portion 31b. The second mirror 2b is tilted as the temperature rises due to the difference in linear expansion coefficient between the magnesium die casting and the resin. The direction of the inclination angle of the second mirror 2b is controlled by the thickness of a plate-like object made of a different material for the mounting portion 31b.

  Here, the second mirror 2b transmits the beam of the red (R) laser 1a and reflects the beam of the green (G) laser 1b and the beam of the blue (B) laser 1c, but the second mirror 2b. The red (R) laser 1a beam may be reflected, and the green (G) laser 1b beam and the blue (B) laser 1c beam may be transmitted. A prism may be used instead of the second mirror 2b. In the present embodiment, the second mirror 2b only needs to be attached to the two locations of the attachment portion 31a and the attachment portion 31b by a known means or method such as an adhesive or a spring.

  In addition, according to the present embodiment, since the optical axis shift can be suppressed by improving the local structure (for example, the mounting portion) in the vicinity of the second mirror 2b, the basic structure of the casing (case) is greatly increased. There is an effect that there is no need to change.

  FIG. 7 shows the mounting structure of the second mirror 2b according to the second embodiment. The mounting portion 32a and the mounting portion 32b are provided with three projections 33a to 33c so that the surface of the second mirror 2b can be stably attached to the case 9. Since the second mirror 2b is stably attached, the optical axis is not displaced. In this figure, the mounting portion 32a is provided with two projections 33a and 33b and the mounting portion 32b is provided with one projection 33c. However, the mounting portion 32a may have one projection and the mounting portion 32b may have two projections.

  The protrusions 33a to 33c are spherical in shape so that the second mirror 2b and the protrusions 33a to 33c can be continuously supported at three points as the temperature rises. It has a structure that does not occur.

  FIG. 8 shows the mounting structure of the second mirror 2b according to the third embodiment. Cylindrical protrusions 35a and 35b are provided on the attachment portion 34a and the attachment portion 34b so that the surface of the second mirror 2b can be stably attached to the case 9. As the temperature rises, the second mirror 2b and the projections 35a and 35b are in continuous contact with each other, and the second mirror 2b is stably attached so that the optical axis is not displaced. The columnar projection includes a projection showing a part of a columnar shape such as a semi-columnar projection as shown in FIG.

  FIG. 9 shows the mounting structure of the second mirror 2b according to the fourth embodiment. As in the third embodiment, the mounting portion 36a and the mounting portion 36b are provided with cylindrical or semi-cylindrical projections 37a and 37b so that the surface of the second mirror 2b can be stably attached to the case 9. is there. A difference from the third embodiment is that a portion 38 having a U-shaped horizontal cross-sectional structure of the mounting portion 36b made of a material different from that of the mounting portion 36a is provided, and the case 9 is sandwiched. By sandwiching the case 9 with the attachment portion 36b, the attachment portion 36b can be securely attached to the case 9, and the adhesive or the like for fixing the attachment portion 36b at the time of attachment can be reduced.

  Here, the adhesive or the like that fixes the attachment portion 36b at the time of attachment has a linear expansion coefficient different from that of the case 9 or the like, and thus causes the second mirror 2b to tilt in an unnecessary direction when the temperature rises. If the adhesive is reduced or the adhesion is only for preventing the attachment portion 36a from coming off, the factor of tilting the second mirror 2b in an unnecessary direction can be reduced. It has a structure with little optical axis deviation. Instead of the mounting adhesive, the first mirror 2a and the second mirror 2b may be pressed and attached to the case 9 using a spring.

  As described above, the description has been given with respect to when the temperature rises. However, the second mirror 2b can be tilted in the opposite direction even when the temperature falls. That is, when the second mirror 2b is tilted 32 according to the optical axis shift 26 due to the temperature drop and the environmental temperature drop of the red (R) laser 1a, green (G) laser 1b and blue (B) laser 1c. The optical axis deviation 26 can be almost eliminated. With this second mirror 2b mounting structure, it is possible to provide a scanning image display apparatus including the laser light source module 100 in which the optical axis deviation 26 is eliminated and the relative positional deviation of the laser spot on the screen 109 is reduced.

  Since the mounting portion 31b can reduce the relative deviation of the spot on the screen only by using a member different from the material (linear expansion coefficient) of the other mounting portion 31a, the laser light source module 100, which is simple and low-cost, and an optical module. 1 can be provided.

  In the above embodiment, the green (G) laser 1b, which is a green laser, and the blue (B) laser 1c, which is a blue laser, have substantially the same laser structure, whereas the red (R) laser 1a, which is a red laser, The description has been given focusing on the structural difference that the heat sink length 22a is about twice as long as the other green (G) laser 1b and blue (B) laser 1c due to the structure of the laser. However, it is not necessary to limit the classification to the red laser and the set of the green laser and the blue laser, and some laser structures in the plurality of lasers are different from the other laser structures in terms of temperature environment. In that case, the technical idea of the present invention is applicable.

In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.
Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files for realizing each function can be stored in a recording device such as a memory, a hard disk, an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.
Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

  DESCRIPTION OF SYMBOLS 1a ... Red (R) laser, 1b ... Green (G) laser, 1c ... Blue (B) laser, 2a ... 1st mirror, 2b ... 2nd mirror, 9 ... Case, 10 ... Stem base, 11 ... Stem Cover, 12 ... Window, 13 ... Lead, 14 ... Heat sink, 15 ... Submount, 16 ... Laser chip, 17 ... Wire, 18 ... Sealing material, 19 ... Light emitting point, 20 ... Light emitting point, 21a ... Light emitting point displacement 21b: Displacement of light emission point, 21c: Displacement of light emission point, 22: Length, 23: Optical axis, 24: Optical axis, 25: Optical axis, 26: Optical axis deviation, 31a: Mounting part, 31b: Mounting part, 32 ... Inclination, 32a to 32b ... Mounting portion, 33a to 33c ... Protrusion, 34a to 34b ... Mounting portion, 35a to 35b ... Protrusion, 36a to 36b ... Mounting portion, 37a to 37b ... Protrusion, 38 ... U-shaped Part to become 100 ... Laser light source module DESCRIPTION OF SYMBOLS 101 ... Optical module, 102 ... Control circuit, 103 ... Video signal processing circuit, 104 ... Laser light source drive circuit, 105 ... Scanning mirror drive circuit, 106 ... Front monitor signal detection circuit, 109 ... Screen, 111 ... 1/4 wavelength plate , 112 ... an angle of view expansion element, 113 ... a scanning mirror, 114 ... a front monitor, 115 ... a reflection mirror, 116 ... an image input signal.

Claims (10)

In an optical module that mounts a plurality of lasers and irradiates light beams from the plurality of lasers,
A mirror that transmits the first laser and reflects the second laser and the third laser;
The optical module is characterized in that the mirror is attached with a plurality of attachment portions different in at least one of material and thickness. In an optical module that mounts a plurality of lasers and irradiates light beams from the plurality of lasers,
A mirror that reflects the first laser and transmits the second laser and the third laser;
The optical module is characterized in that the mirror is attached with a plurality of attachment portions different in at least one of material and thickness. In claim 1 or claim 2,
The optical module, wherein the first laser is a red laser, the second laser is a green laser, and the third laser is a blue laser. In claim 1 or claim 2,
The optical module is characterized in that the mirror is mounted at two mounting portions of two different materials. In claim 1 or claim 2,
An optical module, wherein the mirror is mounted at two locations by two mounting portions made of materials having different linear expansion coefficients. In any one of Claims 1 thru | or 5,
The plurality of attachment portions are two attachment portions in which one attachment portion of the mirror is made of metal and the other attachment portion is made of resin. In any one of Claims 1 thru | or 6,
The plurality of attachment portions have three projections. In any one of Claims 1 thru | or 6,
The plurality of attachment portions have columnar protrusions. In any one of Claims 1 thru | or 8,
At least one mounting portion of the plurality of mounting portions has a U-shaped portion that sandwiches the case of the optical module. An optical module according to any one of claims 1 to 9,
A controller for receiving an image and controlling the optical module;
A scanning-type image display apparatus, wherein an image is displayed by controlling light emission of the laser.